Molecular Microbiology Research 2024, Vol.14, No.5, 248-258 http://microbescipublisher.com/index.php/mmr 251 3.3 Signal transduction and communication Signal transduction and communication in the rhizosphere involve complex chemical signaling between plants and microbes. Plants release root exudates that attract beneficial microbes, which in turn produce signaling molecules like N-Acyl homoserine lactones (AHLs) and other quorum-sensing compounds. These signals regulate microbial community structure and function, enhancing plant-microbe interactions (Hakim et al., 2021). Additionally, PGPR can modulate plant hormone levels, such as auxins and cytokinins, through signaling pathways, thereby promoting plant growth and stress resilience (Nadeem et al., 2014; Kumar et al., 2022). 4 Impact on Kiwifruit Health 4.1 Enhancement of nutrient uptake The rhizosphere microbial community plays a crucial role in enhancing nutrient uptake in kiwifruit plants. Long-term organic fertilization has been shown to improve the productivity of kiwifruit by increasing the diversity and network complexity of rhizosphere microbes. This includes an increase in plant growth-promoting bacteria such as Pseudomonas, Chrysosporium, and Burkholderia, which are positively correlated with fruit yield and quality (Liu et al., 2020). Additionally, intercropping with Vicia sativa L. has been found to significantly enhance soil moisture, microbial community, enzyme activity, and nutrient content in the rhizosphere, leading to improved plant growth metrics such as plant height, stem girth, and chlorophyll content (Qiuping et al., 2021). 4.2 Disease suppression 4.2.1 Biological control agents Biological control agents (BCAs) are an effective strategy for suppressing kiwifruit diseases. Within the rhizosphere microbial community, beneficial microorganisms significantly improve plant health and productivity by enhancing microbial diversity, promoting nutrient uptake, and inhibiting pathogens (Gupta et al., 2019). The mechanism by which these microbes enhance plant resistance through improved rhizosphere microbial community structure and function is illustrated (Figure 2). Several strains of Streptomyces, including Streptomyces racemochromogenes W1SF4, Streptomyces sp. W3SF9, and S. parvulus KPB2, have shown strong antibacterial activity against the kiwifruit bacterial canker pathogen Pseudomonas syringae pv. actinidiae (Psa). These strains also demonstrate excellent colonization ability in the kiwifruit rhizosphere and phyllosphere, making them promising candidates for biological control (Kim et al., 2019). The study by Gupta et al. (2019) highlights the positive impact of microorganisms on kiwifruit health through disease suppression mechanisms. BCAs inhibit the growth and spread of pathogens by competing for nutrients and space, producing antimicrobial substances, and inducing systemic resistance in plants. The figure details how these microorganisms enhance the diversity and stability of the rhizosphere microbial community, boosting the disease resistance of kiwifruit plants, thereby reducing disease incidence and improving overall plant health and yield. 4.2.2 Induced systemic resistance (ISR) Induced systemic resistance (ISR) is another mechanism through which rhizosphere microbes can enhance kiwifruit health. Sulfur-induced resistance has been shown to significantly reduce the severity of kiwifruit bacterial canker. The application of sulfur, combined with organic fertilizer, not only decreased disease incidence but also increased the diversity and beneficial microbial taxa in the rhizosphere (Table 1), such as Acidothermus and members of the Acidobacteriaceae family (Yang et al., 2022). Table 1 shows the effects of different sulfur treatments on the microbial characteristics of kiwifruit rhizosphere soil. Sulfur-induced systemic resistance (ISR) significantly enhances the disease resistance of kiwifruit by increasing the proportion of beneficial microbes. The data in Table 1 indicate that the appropriate application of sulfur can enhance the diversity and functionality of microbial communities, particularly by boosting the ISR mechanism, thereby strengthening the plant's resistance to pathogens.
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